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Embedded Android Workshop

Part 3 - Native Android user-space

Linaro Connect Asia 2013

Karim Yaghmour@karimyaghmour

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About

● Author of:

● Introduced Linux Trace Toolkit in 1999● Originated Adeos and relayfs (kernel/relay.c)● Training, Custom Dev, Consulting, ...

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Native Android User-Space

● Filesystem layout● Architecture vs. filesystem● Build system and filesystem● adb● Command line● Init● ueventd● Boot logo● Bionic● Tiny Android● Legacy integration

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1. Filesystem layout

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● /acct => Control Group mount point (Documentation/cgroups.txt)● /cache => cache flash partition● /d => Symlink to /sys/kernel/debug● /data => Android's “/data” filesystem● /dev => Device nodes● /etc => Symlink to /system/etc● /mnt => Temporary mount point● /proc => procfs● /root => unused● /sbin => eventd and adbd● /sdcard => SD card mountpoint● /sys => sysfs● /system => Android's “/system” filesystem● /vendor => Symlink to /system/vendor

1.1. Root directory

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1.1. /system

● /app => Stock apps installed● /bin => Native binaries and daemons● /etc => Configuration files● /fonts => TTFs● /framework => Android framework .jar files● /lib => Native libraries● /usr => Miniature “/usr”● /xbin => Optional/Extra binaries

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1.2. /data

● /anr => ANR traces● /app => App install location● /app-private => Protected apps● /backup => For Backup Manager● /dalvik-cache => Dalvik DEX cache● /data => App data● /dontpanic => Last panic output (console + threads) for “dumpstate”● /local => Shell-writable space● /misc => Misc. data (wifi, vpn, bluetooth, ...)● /property => Persistent system properties (country, lang., ...)● /secure => Secure Android data available● /system => System data

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2. Architecture vs. filesystem

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3. Build system and filesystem

● Build templates● BUILD_EXECUTABLE = /system/bin● BUILD_SHARED_LIBRARY = /system/lib● BUILD_PACKAGE = /system/app

● Default rights and ownership● system/core/include/private/android_filesystem_config.h● User IDs / names● android_dirs struct● android_files struct

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4. adb

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4.1. What adb can do

● See online help for full details● Managing device connections● Remote commands:

● shell● log dumping● bug reports● port forwarding● dalvik debugging

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● Filesystem commands● push● pull● sync● install / uninstall

● State-altering commands● reboot● run as root● switching connection type● controlling the emulator

● Tunneling PPP

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5. Command line

● Shell:● NetBSD shell up to 2.3/GB● MirBSD Korn shell since 4.0/ICS

● Toolbox:● Traditional Linux commands● Global properties● Input events● Services control● Logging● ioctl● Device wiping● etc.

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● In aosp:● /system/core/toolbox

● In filesystem:● /system/bin/toolbox

● Provides

alarm date getevent insmod ls mv powerd renice schedtop smd top dd getprop ioctl lsmod nandread printenv rm sendevent start umount cat hd ionice lsof netstat ps rmdir setconsole stop uptime chmod df id kill mkdir newfs_msdos r rmmod setkey sync vmstat chown dmesg ifconfig ln readtty rotatefb setprop syren watchprops cmp exists iftop log mount notify reboot route sleep wipe

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● logcat● netcfg● debuggerd

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6. Init

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6.1. Config files

● Location:● /init.rc● /init.[board].rc

● Semantics:● actions

– Property triggers– Commands

● services (not related to system services or apps)– Parameters

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6.2. Global properties

● /dev/socket/property_service● /dev/__properties__● foo.bar.property● ro.*● persist.* => /data/property● ctl.*● net.change

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● Std files:● /system/build.prop● /default.prop

● Other files:● /system/default.prop● /data/local.prop

● Code:– property_get("dalvik.vm.heapsize", heapsizeOptsBuf+4, "16m");

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7. ueventd

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7.1. /ueventd.rc

/dev/null 0666 root root

/dev/zero 0666 root root

/dev/full 0666 root root

/dev/ptmx 0666 root root

/dev/tty 0666 root root

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8. Boot logo

$ cd device/acme/coyotepad

$ convert ­depth 8 acmelogo.png rgb:acmelogo.raw

$ rgb2565 ­rle < acmelogo.raw > acmelogo.rle

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9. Bionic

● In aosp:● /bionic

● In filesystem:● /system/lib

● Provides:● libc● libm● libdl● libstd++● libthread_db● linker

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10. Tiny Android

$ BUILD_TINY_ANDROID=true make ­j4

● 3MB filesystem● Minimal root fs● init● toolbox + shell● adb● bionic + utility libs● No “system/framework/”● No “system/app”

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11. Legacy Integration

● What if I ... ?:● have been using my custom rootfs forever● really need glibc● have a huge stack based on “legacy Linux”● don't want to deal with AOSP's build system● want BusyBox● want to unify with a std Linux desktop● need things the AOSP doesn't provide● have a ton of Linux drivers and want those to be used by Android● ...

● Know this: filesystem integration is trivial:● Change build system to copy your custom rootfs● Change init scripts to start you own daemons● Use sockets to communicate

● Know this too: std Linux desktop integration is NOT

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Thank you ...

karim.yaghmour@opersys.com